This invention relates to methods and arrangements for seat occupancy recognition in motor vehicles.
For many reasons, knowing whether a vehicle seat is occupied and the nature of the occupancy is very important. If, for example, a child seat is in an incorrect position on a vehicle seat, triggering of an airbag may have serious consequences for a child in the child seat. Knowledge of the location of a person on a vehicle seat is of great interest since it is important to the function of an airbag that a minimum distance should be assured between the occupant and the airbag at the beginning of airbag release so that there will be enough time for the airbag to expand in a collision. Also, the airbag should be released only if the vehicle seat really is occupied, since repair of the released airbag is very expensive. Furthermore, comfort functions may be adjusted according to seat occupancy, like an air-conditioning unit or a fan which may be operated according to whether passenger seat is occupied or not.
German Patent No. 38 02 159 discloses a seat occupancy recognition arrangement for motor vehicles having adjustable seats in which occupancy of a vehicle seat is determined by a comparator which operates a switch, by displacement transducers detecting the position of the seat relative to the vehicle and the parts of seat relative to each other, and by a contact-free range finder measuring a distance from a seat surface or a part of a seat surface to a part of the vehicle on which a range finder is mounted. The comparator calculates a distance from the surface of the vehicle seat to the range finder sensor from position data of the displacement transmitters, compares the distance with that determined by the range finder and, if the readings coincide, triggers the switch. The range finder is preferably in the form of an ultrasonic or infrared sensor which transmits an ultrasonic or infrared signal toward the vehicle seat and receives a signal reflected from that direction by a surface of a person sitting on the seat or, if the seat is unoccupied, from the back rest of the seat, by which the seat occupancy condition may be inferred from the transit time of the signal.
U.S. Pat. No. 5,330,226 discloses a seat occupancy recognition arrangement in which an infrared sensor is mounted in the roof above the seat. The infrared sensor has a plurality of fields of vision by which the position of an occupant relative to the airbag is determined so that the airbag, when released, can be suitably triggered without injuring the occupant.
German Offenlungsschrift No. 41 10 702 discloses a seat occupancy recognition arrangement for actuating a seat heater in which a seat heating conductor mounted in the seat surface and heatable by electric current forms the first electrode of a capacitive seat occupancy sensor consisting of two electrodes.
A disadvantage of all prior art occupant detecting arrangements is that the vehicle occupants are continuously exposed to sources of radiation. Since the effects of long-term exposure to electromagnetic radiation, or to ultrasonic waves, are much in dispute, there is a danger that the well-being of the occupants may be impaired, or even that they may be injured, by a continuous exposure to radiation.